Gear teeth are often used in mechanisms, in splined engagement with closely fitting channels, in order to reliably provide axial movement within a drive mechanism base. The splined engagement advantageously permits ready removal of connected components for service and/or parts replacement. Connections between teeth and co-fitting channels generally take advantage of increased surface area contact afforded by multiple toothed engagement and the strength of unitary metal element engagements. Despite such advantages, splined engagements of teeth and channels are subject to lateral wear and tear in the direction of limited axial teeth travel within the channels.
Vehicular clutch drive plates and particularly those used in automotive transmissions and torque converters exemplify gear teeth splined engagements subject to such detrimental wear. The clutch drive plates are usually lined with friction materials and are assembled to unlined driven plates to form a clutch pack. Such a clutch pack is typically compressed by hydraulic pressure within a torque converter to create a solid connection between drive and driven members. This construction is termed “lock up” and eliminates the 6-7% loss of efficiency inherent in torque converters.
In a typical construction, the torque converter front cover is internally splined with mating grooves for the splined teeth of a drive plate. In this configuration, an externally splined drive plate, with a friction material bonded to its surface, is assembled within the splined front cover. A driven plate, with internal splines, slidingly engages the driven member, typically, the turbine assembly of the torque converter. Though the teeth of a clutch plate are closely fitted with exacting tolerances there remains the very small separations required to enable sliding engagement between the teeth and co-fitting channels. After numerous engagements and disengagements during use, the relatively sharp external teeth of the drive plate may cut fretting wear into the engaging surfaces of the front cover. In addition, the teeth themselves often also exhibit excessive wear.
The result of the undue wear is erratic clutch engagement and undesirable noise. In addition, excessively fretted parts must be replaced at considerable expense. The above described conditions typically occur in the covers of torque converters used in various models of vehicle automatic transmissions, such as those of the Ford Motor company manufacture, which are configured with the splined connection between clutch plate teeth and torque converter covers.
U.S. Pat. No. 7,296,666 issued to Michael Morin describes the Ford Motor Company transmissions and torque converters susceptible to mechanical stress and wear, as described, and provides a heavy duty torque converter cover with a machined internal spline configuration and an asserted increase in splined tooth engagement with a mating friction plate and reduced wear. The disclosure of this patent is incorporated herein in its entirety as showing the present state of the art of expedients used to reduce mechanical stress and wear of torque converters and transmissions.
In other prior art, such as U.S. Pat. No. 3,760,921 (Gillespie) and, U.S. Pat. No. 4,967,890 (Landa) and British Patent GB 1522825, the sides or flanks of the teeth in an automatic transmission are splayed, extended or bent to reduce the incidence of sharp edges. As a result, the teeth in these patents present a smoother or larger surface to the lateral engaging surfaces of the channels in the direction of travel. However, these lateral extensions introduce detrimental structural problems of increased tooth spacing and reduced number of engaging teeth in the design of the clutch plates (GB 1522825). The Landa and Gillespie patents describe modification of existing edge contact without however presenting any new contact area to compensate for wear in failure-prone areas. The structures disclosed therein cannot bridge existing or potential wear points due to limited material available for tooth edge modification.